Method for preparing layered perovskite compound thin film with organic ammonium layers and inorganic layers

ABSTRACT

A method for preparing a layered perovskite compound thin film having a film thickness and structure controlled at a monomolecular layer and capable of combining various layered perovskite compounds at the level of a monomolecular layer. The method a superlattice structure represented by the general formula A 2 MX 4  where A is an organic ammonium molecule, M is a group 4 element or transition metal and X is halogen layers of organic ammonium molecule “A” and layers of inorganic halide “MX 4 ” are alternately stacked. A monomolecular film of an organic amine hydrohalic acid salt having a long-chain alkyl group is spread out on the surface of a water solution of an inorganic halide MX 2  and a methylamine hydrohalic acid salt. By leaving the monomolecular film, a layered perovskite compound monomolecular film is formed on the surface of the water solution. This layered perovskite monomolecular film is transferred and stacked onto a substrate on a one by one basis by using the Langmuir-Blodgett method.

TECHNICAL FIELD

[0001] The present invention relates to a method for preparing a layeredperovskite compound thin film with organic ammonium layers and inorganiclayers, and a layered perovskite compound thin film with organicammonium layers and inorganic layers prepared thereby in which theorganic ammonium molecule contains a functional chromophore.

BACKGROUND ART

[0002] It is known that a layered perovskite compound has a superlatticestructure in which an organic layer and an inorganic layer arealternately stacked, and exhibits various interesting properties usefulfor low-dimensional semiconductors, magnetic bodies, luminous bodies orthe like, depending on the type of inorganic halide layer. In addition,it is suggested that the layered perovskite compound has the potentialof providing new functional materials capable of bringing out combinedfunctionalities of organic layers and inorganic layers (M. Era, K.Maeda, and T. Tsutsui, Chemistry Letters, 1235-1236, 1997).

[0003] One of known layered perovskite compounds has a superlatticestructure which is represented by the general formula A₂MX₄ where A isan organic ammonium molecule, M is a group 4 element or transition metaland X is halogen (Cl, Br, I), and in which a layer of organic ammoniummolecule “A” and a layer of inorganic halide “MX₄” are alternatelystacked (see FIG. 10 showing a schematic diagram thereof). Further,another known layered perovskite compound has a superlattice structurewhich is represented by the general formula A₂MX₄, where A is organicammonium ions, M is divalent rare earth metal cations and X is halogen(Cl, Br, I), and in which a layer of organic ammonium molecule “A” and alayer of inorganic halide “MX₄” are alternately stacked (Japanese PatentLaid-Open Publication No. Hei 10-316685).

[0004] A conventional method for preparing a thin film from such layeredperovskite compounds includes one method (a casting method orspin-coating method) in which a crystal of a layered perovskite compoundor a mixture of an organic amine hydrohalic acid salt and an inorganichalide MX₂ is dissolved in an organic solvent and then a thin film isformed from the resulting solution, and another method (a two-sourcedeposition method) in which an organic amine hydrohalic acid salt and aninorganic halide MX₂ are deposited simultaneously in vacuo.

[0005] Heretofore, as a method for depositing monomolecular films, therehas been known the Langmuir-Blodgett method (LB method) used formanufacturing organic thin films. Japanese Patent Laid-Open PublicationNo. Hei 11-140656 disclosed a method for manufacturing an inorganic thinfilm in which monomolecular films are accumulated with controlling thecomposition and arrangement of metal elements by using theLangmuir-Blodgett method to form an organic thin film, and then theorganic component of the organic thin film is decomposed and removed toform an inorganic thin film. However, such a method has not beensuccessfully used for preparing layered perovskite compound thin films.

[0006] As shown in FIG. 9, the Langmuir-Blodgett method is a techniquefor preparing a thin film having a film thickness and structurecontrolled at the level of a monomolecular layer by forming amonomolecular film of amphipathic molecules on the water andtransferring it onto a substrate (see “Physics and ChemistryDictionary-5th Edition” published by Iwanami Shoten).

DISCLOSURE OF INVENTION

[0007] (Problem to be solved by the Invention)

[0008] For using the above layered perovskite compound with organicammonium layers and inorganic layers as device materials, it is acritical task to control a film thickness and structure stringently atthe level of a monomolecular layer. Further, if such layered perovskitecompounds can be combinedly formed at the level of a monomolecularlayer, it would open the way to develop various materials having higherperformance. However, the conventional techniques for preparing layeredperovskite compounds have not been able to prepare such a thin filmhaving a film thickness and structure controlled at the level of amonomolecular layer.

[0009] Therefore, it is an object of the present invention to provide anovel method for preparing a layered perovskite compound thin film withorganic ammonium layers and inorganic layers which has a film thicknessand structure controlled at the level of a monomolecular layer, and toprovide a layered perovskite compound thin film with organic ammoniumlayers and inorganic layers which has a novel function useful fordevices, through this method.

[0010] (Means for solving the problem)

[0011] The inventor has found a method for forming a monomolecular filmof an organic-inorganic layered perovskite compound on the surface of awater solution. Based on this method and applying the Langmuir-Blodgettmethod, the inventor has made it possible to prepare a layeredperovskite organic-inorganic superlattice material having a filmthickness and structure controlled at the level of a monomolecularlayer. Further, in combination with this method, the inventor hasachieved to introduce a chromophore into the organic layers so as toallow the layered perovskite organic-inorganic superlattice material tobe applied to electroluminescence (EL) devices.

[0012] More specifically, according to a first aspect of the presentinvention, there is provided a method for preparing a layered perovskitecompound thin film with organic ammonium layers and inorganic layerswhich has a superlattice structure represented by the general formulaA₂MX₄ where “A” is an organic ammonium molecule, “M” is a group 4element or transition metal and “X” is halogen (Cl, Br, I), and in whicha layer of organic ammonium molecule “A” and a layer of inorganic halide“MX₄” are alternately stacked, characterized in that an organic solventsolution having dissolved therein an organic ammonium molecule or amixture of an organic ammonium molecule and an inorganic halide isdropped onto to the surface of a water solution having dissolved thereina water-soluble organic ammonium molecule and an inorganic halide toform a monomolecular film of an organic amine hydrohalic acid salthaving a long-chain alkyl group and simultaneously to react the formedmonomolecular film with the inorganic halide in the water solution so asto form a monomolecular film of a layered perovskite with organicammonium layers and inorganic layers on the surface of the watersolution, and then the formed monomolecular film is transferred onto asubstrate by using the Langmuir-Blodgett method.

[0013] The group 4 element herein is Ge, Sn or Pb, and the transitionmetal is Cr, Mn, Fe, Co, Ni, Cu, Zn or Cd. The inorganic halide is acompound represented by the chemical formula MX₂ where M is a group 4element or transition metal and X is halogen (Cl, Br, I). The substratefor the monomolecular film to be transferred thereon may be selectedfrom the group consisting of a silicon substrate, a metal plate, a glassplate, a fused quartz substrate, and an inorganic compound singlecrystal substrate.

[0014] In the method according to the first aspect of the presentinvention, the organic ammonium molecule to be dissolved in the watersolution may be a water-soluble alkylamine hydrohalic acid saltC_(n)H_(2n+1)NH₃X, and the organic ammonium molecule to be dissolved inthe organic solvent solution may contain a non-water-soluble alkylaminehydrohalic acid salt C_(n)H_(2n+1)NH₃X. The water-soluble alkylaminehydrohalic acid salt C_(n)H_(2n+1)NH₃X can facilitate the formation ofthe layered perovskite monomolecular film on the surface of the watersolution.

[0015] Further, the non-water-soluble alkylamine hydrohalic acid saltC_(n)H_(2n+1)NH₃X to be dissolved in the organic solvent solution may bea dococylamine hydrohalic acid salt C₂₂H₄₅NH₃X. The dococylaminehydrohalic acid salt C₂₂H₄₅NH₃X having a long-chain alkyl group allows astable monomolecular film to be formed on the water solution.

[0016] In the method according to the first aspect of the presentinvention, the organic solvent may be chloroform or a mixture ofchloroform and dimethylformamide. The dimethylformamide added to thesolvent allows the hardly-soluble inorganic halide to be sufficientlydissolved in the solvent solution.

[0017] Further, in the method according to the first aspect of thepresent invention, the organic ammonium molecule “A” may be an organicammonium containing a functional chromophore. The organic ammoniumcontaining the functional chromophore allows the layered perovskitecompound thin film with organic ammonium layers and inorganic layers tobe provided with the organic layers having a useful function.

[0018] In this case, the organic ammonium molecule to be dissolved inthe organic solvent may be an organic ammonium containing anon-water-soluble functional chromophore. The chromophore devoid of anyelectrically insulative alkyl chain allows the layered perovskitecompound thin film to have high conductivity. This advantageouslyprovides an electronic function suitable for EL devices and otherelectronic devices.

[0019] Further, the functional chromophore may be azobenzene chromophoreor salicyliden aniline chromophore. The azobenzene chromophore orsalicyliden aniline chromophore exhibiting a photochromic reactionallows the property of the layered perovskite to be opticallycontrolled.

[0020] According to a second aspect of the present invention, there isprovided a method for a layered perovskite compound thin film withorganic ammonium layers and inorganic layers, characterized in that aplurality of layered perovskite compound thin films are prepared by themethod according to the first aspect of the present invention, whereinat least two of the layered perovskite compound thin films are differentin at least either one of the kinds of the inorganic layer and organicammonium layer, and wherein the formed layered perovskite compound thinfilms are combinedly stacked in increments of a monomolecular layer.There are various layered perovskites capable of exhibiting an optical,magnetic or semiconductive characteristic. Thus, according to thismethod, a thin film having a new functionality can be prepared bycombining such layered perovskites at the level of a monomolecularlayer.

[0021] According to a third aspect of the present invention, there isprovided a layered perovskite compound thin film with organic ammoniumlayers and inorganic layers prepared by the method according to eitherone of the first and second aspects of the present invention, which hasa superlattice structure represented by the general formula A₂MX₄ where“A” is an organic ammonium molecule, “M” is a group 4 element ortransition metal and “X” is halogen (Cl, Br, I), and in which a layer oforganic ammonium molecule “A” and a layer of inorganic halide “MX₄” aresuperimposed alternately, wherein the organic ammonium molecule “A” isan organic ammonium containing a functional chromophore. When forming acomposite layered perovskite compound thin film, the property orfunction of the inorganic or organic layer in each of the layeredperovskites can be combined at the level of a monomolecular layer.

[0022] In the layered perovskite compound thin film with organicammonium layers and inorganic layers according to the third aspect ofthe present invention, the functional chromophore may be azobenzenechromophore or salicyliden aniline chromophore. The photochromicchromophore exhibiting a certain photochromic reaction depending onlights having different wavelengths allows the property of theparticular layered perovskite in the composite layered perovskitecompound thin film to be optically controlled.

[0023] Further, the inorganic halide may be PbBr₂ or CuBr₂. ThePbBr₂-based layered perovskite exhibits semiconductive properties, andthe CuBr₂-based layered perovskite exhibits ferromagnetic properties

BRIEF DESCRIPTION OF DRAWINGS

[0024]FIG. 1 is an explanatory conceptual diagram of a principle offorming a monomolecular film of an organic amine hydrohalic acid salthaving a long-chain alkyl group on the surface of a water solution.

[0025]FIG. 2 is a graph showing an absorption spectrum of a layeredperovskite compound thin film prepared in an example 1.

[0026]FIG. 3 is a graph showing an X-ray diffraction profile of alayered perovskite compound thin film prepared in an example 2.

[0027]FIG. 4 is a conceptual diagram showing the layer structure of anorganic ammonium-containing PbBr-based layered perovskite.

[0028]FIG. 5 is a graph showing an absorption spectrum of a layeredperovskite compound thin film prepared in an example 3.

[0029]FIG. 6 is a graph showing an absorption spectrum of a layeredperovskite compound thin film prepared in an example 4.

[0030]FIG. 7 is a graph showing an absorption spectrum of a layeredperovskite compound thin film prepared in an example 5.

[0031]FIG. 8 is a graph showing an absorption spectrum of a layeredperovskite compound thin film in which monomolecular films prepared inan example 6 are superimposed on a one by one basis.

[0032]FIG. 9 an explanatory schematic diagram showing one embodiment fortransferring a monomolecular film onto a substrate by using theLangmuir-Blodgett method.

[0033]FIG. 10 is a schematic diagram of a superlattice structure of anorganic ammonium-containing inorganic layered perovskite compound.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] With reference to FIG. 1, a method according to the presentinvention for preparing a layered perovskite thin film in combinationwith the Langmuir-Blodgett method will now be described in detail. Acommercially available LB film depositing apparatus can be used forpreparing an LB film. For a start, as shown in FIG. 1 (a), a watersolution having dissolved therein an inorganic halide MX₂ and alkylaminehydrohalic acid salt C_(n)H_(2n+1)NH₃X as an organic ammonium moleculewhich constitute perovskite is prepared.

[0035] Then, as shown in FIG. 1 (b), a solution formed by dissolvingonly a non-water-soluble organic amine hydrohalic acid salt in anorganic solvent, or a solution formed by dissolving a non-water-solubleorganic amine hydrohalic acid salt, a water-soluble organic aminehydrohalic acid salt (e.g. methylamine hydrohalic acid salt) and aninorganic halide MX₂ in an organic solvent is prepared. Then, thissolution is dropped onto the surface of the water solution and thesurface area of the dropped solution on the surface of the watersolution is narrowed to form a monomolecular film of thenon-water-soluble organic amine hydrohalic acid on the water solution.By adding the inorganic halide MX₂, a desired layered perovskite thinfilm can be more reliably formed.

[0036] Then, as shown in FIG. (c), the monomolecular film is left on thesurface of the water solution to react the monomolecular with theinorganic halide in the water solution so as to form a layeredperovskite compound monomolecular film. This reaction is represented bythe reaction formula 2RNH₃X+MX₂→(RNH₃)₂MX₄.

[0037] Then, the formed layered perovskite monomolecular film istransferred and stacked on a one by one basis through theLangmuir-Blodgett method to provide a layered perovskite compound thinfilm having a film thickness and structure controlled at the level of amonomolecular layer.

EXAMPLE

[0038] Example 1

[0039] 1.5 liters of water solution (concentration: 10⁻⁴ mol/l) havingdissolved therein lead bromide as an inorganic halide MX₂ andmethylamine hydrobromide as an organic ammonium molecule was poured intoa vessel and was kept in a stable state. Then, 2 ml of organic solventsolution (concentration: 10⁻⁴ mol/l) having dissolved thereindococylamine hydrobromide with chloroform as an organic solvent wasdropped onto the surface of the water solution.

[0040] The organic solvent was completely evaporated just after thedropping. After the vaporization, when the monomolecular film wascompressed to increase its surface pressure up to 30 mN⁻¹, anorganic-inorganic layered perovskite compound monolayer film of dococylammonium-lead bromide represented by the molecular formula(C₂₂H₄₅NH₃)₂PbBr₄ was formed on the surface of the water solution. Afused quartz subjected to a hydrophobic treatment withhexamethyldisilazane was used as a substrate. The formed monolayer filmwas transferred and stacked onto the substrate on a one by one basis soas to form a multi-layer organic-inorganic layered perovskite compoundfilm.

[0041]FIG. 2 shows an absorption spectrum of the lead bromide-basedlayered perovskite (C₂₂H45NH₃)₂PbBr₄ thin film prepared in this example.The thin film exhibits the sharp exciton absorption characteristic ofthe lead bromide-based layered perovskite in the vicinity of 390 nmwavelength. This proves that a lead bromide-based layered perovskitecompound PbBr₄ thin film is obtained.

[0042] From the absorbance of the exciton absorption, it was alsoverified that the thin film was formed by stacking one monomolecularlayer for each stack operation. Further, it was verified that thislayered perovskite monomolecular layer could be stacked to form amulti-layer so as to provide a desired thin film having a film thicknesscontrolled at the level of a monomolecular layer, because the excitonabsorption was increased in proportion to the number of the stackoperations.

[0043] Example 2

[0044] An organic solvent containing about 10 volume % ofdimethylformamide added in chloroform was used as a substitute for thechloroform used as an organic solvent in the example 1. Both ofdococylamine hydrobromide C₂₂H₄₅NH₃Br and lead bromide are dissolved inthe organic solvent to form an organic solvent solution to be used.

[0045] In this manner, a desired (C₂₂H45NH₃)₂PbBr₄ layered perovskitethin film as in the example 1 could be prepared with excellentreproducibility. FIG. 3 shows an X-ray diffraction profile of a thinfilm formed through ten stack operations. A diffraction peakcorresponding to (0 0 n) of the lead bromide-based layered perovskitewas observed, and a layer pitch of 4.5 nm was calculated from thediffraction peak. This value matches with the layer pitch of the(C₂₂H45NH₃)₂PbBr₄ layered perovskite. FIG. 4 conceptually shows the(C₂₂H45NH₃)₂PbBr₄ layered perovskite structure.

[0046] Example 3

[0047] A thin film was prepared in the same manner as that of theexample 2 except for using CuBr₂ as an inorganic halide. FIG. 5 shows anabsorption spectrum of the obtained thin film. The absorption caused byd-d transition peculiar to copper bromide-based perovskite(C₂₂H45NH₃)₂CuBr₄ was observed in the vicinity of each wavelength of 540nm and 360 nm. This proves that a copper bromide-based layeredperovskite thin film is obtained.

[0048] Example 4

[0049] A layered perovskite compound thin film with organic layershaving a functional chromophore introduced thereinto was prepared. Thethin film was prepared by using an organic ammonium hydrobromidecontaining an azobenzene chromophore represented by the followingformula (1) as the chromophore.

[0050] For preparing the thin film, the organic ammonium hydrobromidecontaining the azobenzene chromophore was used as a substitute for thedococylamine hydrobromide used in the examples 1 and 2. FIG. 6 shows anabsorption spectrum of the thin film prepared by using the organicammonium hydrobromide containing the azobenzene chromophore.

[0051] In case of using the azobenzene chromophore, the absorptionpeculiar to H-aggregation of the azobenzene chromophore was observed inthe vicinity of 330 nm in addition of the exciton absorption of the leadbromide-based layered perovskite compound around 390 nm. From thisspectrum, it was verified that a lead bromide-based layered perovskitecompound thin film with organic layers having the azobenzene chromophoreintroduced thereinto was formed by using the organic ammoniumhydrobromide containing the azobenzene chromophore.

[0052] Example 5

[0053] A salicyliden aniline chromophore represented by the followingformula (2) was used as a substitute for the azobenzene chromophore inthe example 4.

[0054] As shown in FIG. 7, in case of using the salicyliden anilinechromophore, the absorption peculiar to the salicyliden anilinechromophore was observed in the vicinity of each wavelength of 300 nmand 350 nm in addition of the exciton absorption of the leadbromide-based layered perovskite compound around 390 nm. From thisspectrum, it was verified that a lead bromide-based layered perovskitecompound thin film with organic layers having the salicyliden anilinechromophore introduced thereinto was formed.

[0055] Example 6

[0056] In this example, a layered perovskite thin film as amonomolecular-order layer is combinedly stacked on a one by one basis. Acomposite film was prepared by using PbBr₂ and CuBr₂ separately as aninorganic halide for each layered perovskite compound monomolecular filmand stacking the monomolecular film on a one by one basis according toeach process of the examples 2 and 3. FIG. 8 shows an absorptionspectrum of the prepared thin film.

[0057] The exciton absorption of the lead bromide-based layeredperovskite compound and the d-d transition-derived absorption of thecopper bromide-based layered perovskite compound are observed in thevicinity of 390 nm and 540 nm, respectively. It is proved that thisabsorption spectrum is formed by superimposing respective absorptionspectrums of the above two kinds of layered perovskite compoundmonomolecular films.

INDUSTRIAL APPLICABILITY

[0058] As described above, the method of the present invention canprepare the following novel functional compound thin films.

[0059] (1) A layered perovskite thin film having a film thicknesscontrollable at the level of a monomolecular layer.

[0060] (2) A layered perovskite thin film with having organic layershaving a functional chromophore introduced therein prepared by using anorganic amine hydrohalic acid salt containing a functional chromophore.

[0061] (3) A composite thin film composed of combined layered perovskitecompound monomolecular films each having different organic or inorganiclayers prepared by stacking such monomolecular films on a one by onebasis.

What is claimed is:
 1. A method for preparing a layered perovskitecompound thin film with organic ammonium layers and inorganic layers,said layered perovskite compound thin film having a superlatticestructure represented by the general formula A₂MX₄, where A is anorganic ammonium molecule, M is a group 4 element or transition metaland X is halogen (Cl, Br, I), and in which a layer of organic ammoniummolecule A and a layer of inorganic halide MX₄ are alternately stacked,wherein an organic solvent solution having dissolved therein an organicammonium molecule or a mixture of an organic ammonium molecule and aninorganic halide is dropped onto to the surface of a water solutionhaving dissolved therein a water-soluble organic ammonium molecular andan inorganic halide to form a monomolecular film of an organic aminehydrohalic acid salt having a long-chain alkyl group and simultaneouslyto react said formed monomolecular film with said inorganic halide insaid water solution so as to form a monomolecular film of a layeredperovskite with organic ammonium layers and inorganic layers on thesurface of said water solution, and then said formed monomolecular filmis transferred onto a substrate by using the Langmuir-Blodgett method.2. A method for preparing a layered perovskite compound thin film withorganic ammonium layers and inorganic layers as defined in claim 1,wherein said organic ammonium molecule to be dissolved in said watersolution is a water-soluble alkylamine hydrohalic acid saltC_(n)H_(2n+1)NH₃X, and said organic ammonium molecule to be dissolved insaid organic solvent solution contains a non-water-soluble alkylaminehydrohalic acid salt C_(n)H_(2n+1)NH₃X.
 3. A method for preparing alayered perovskite compound thin film with organic ammonium layers andinorganic layers as defined in claim 2, wherein said non-water-solublealkylamine hydrohalic acid salt C_(n)H_(2n+1)NH₃X to be dissolved insaid organic solvent solution is a dococylamine hydrohalic acid saltC₂₂H₄₅NH₃X.
 4. A method for preparing a layered perovskite compound thinfilm with organic ammonium layers and inorganic layers as defined ineither one of claims 1 to 3, wherein said organic solvent is chloroformor a mixture of chloroform and dimethylformamide.
 5. A method forpreparing a layered perovskite compound thin film with organic ammoniumlayers and inorganic layers as defined in either one of claims 1 to 4,wherein said organic ammonium molecule A is an organic ammoniumcontaining a functional chromophore.
 6. A method for preparing a layeredperovskite compound thin film with organic ammonium layers and inorganiclayers as defined in claim 5, wherein said organic ammonium molecule tobe dissolved in said organic solvent is an organic ammonium containing anon-water-soluble functional chromophore.
 7. A method for preparing alayered perovskite compound thin film with organic ammonium layers andinorganic layers as defined in claim 5 or 6, wherein said functionalchromophore is azobenzene chromophore or salicyliden anilinechromophore.
 8. A method for a layered perovskite compound thin filmwith organic ammonium layers and inorganic layers as defined in eitherone of claims 1 to 7, wherein a plurality of layered perovskite compoundthin films are prepared by the method, wherein at least two of saidlayered perovskite compound thin films are different in at least eitherone of the kinds of said inorganic layer and organic ammonium layer, andwherein said formed layered perovskite compound thin films arecombinedly stacked in increments of a monomolecular layer.
 9. A layeredperovskite compound thin film with organic ammonium layers and inorganiclayers prepared by the method as defined in either one of claims 1 to 8,said layered perovskite compound thin film having a superlatticestructure represented by the general formula A₂MX₄, where A is anorganic ammonium molecule, M is a group 4 element or transition metaland X is halogen (Cl, Br, I), and in which a layer of organic ammoniummolecule A and a layer of inorganic halide MX₄ are superimposedalternately, wherein said organic ammonium molecule A is an organicammonium containing a functional chromophore.
 10. A layered perovskitecompound thin film with organic ammonium layers and inorganic layers asdefined in claim 9, wherein said functional chromophore is azobenzenechromophore or salicyliden aniline chromophore.
 11. A layered perovskitecompound thin film with organic ammonium layers and inorganic layers asdefined in claim 9 or 10, wherein said inorganic halide is PbBr₂ orCuBr₂.